Dynamic Random Access Memory (DRAM) cells within semiconductor circuits typically incorporate deep trench storage capacitors. As the lithographic ground rules used to pattern such deep trench storage capacitors continue to diminish with each successive generation of DRAM technology, it is desired to reduce process complexity and to increase manufacturing tolerances. Buried plate diffusion regions are commonly used to connect the plate region of a deep trench storage capacitor array. Current processes for making such buried plate diffusion regions add process steps and process complexity, however, to the cost-sensitive DRAM manufacturing process.
For example, a standard process for manufacturing DRAM trench capacitor buried plates may comprise:
(a) etching a trench in a surface of a substrate; PA1 (b) forming a barrier layer on the trench side wall; PA1 (c) filling the trench with photoresist; PA1 (d) etching the photoresist to a predetermined depth, controlling the depth by the amount of etch time, the depth defining a filled lower region and an exposed upper region; PA1 (e) removing the barrier layer in the upper region to expose the underlying side wall; PA1 (f) stripping the photoresist; PA1 (g) forming a collar on the side wall upper portion, using the barrier layer as a mask in the lower region; and PA1 (h) forming a buried plate diffusion region in the trench lower region, using the collar as a mask for the upper portion.
The above process, using a photoresist fill and etch step, is commonly called a photoresist recess technique. Because the steps of filling with photoresist and etching add process complexity, it is desirable to simplify and shorten the process for formation of buried plate diffusion regions in deep trench storage capacitors by eliminating the photoresist fill and etch steps.
The deficiencies of the conventional methods used to manufacture DRAM deep trench storage capacitors and buried plates in such capacitors show that a need still exists for an improved process. To overcome the shortcomings of the conventional methods, a new process is provided. An object of the present invention is to simplify and shorten the process for formation of buried plate diffusion regions in deep trench storage capacitors. A related object is to eliminate the photoresist fill and etch steps typically used in conventional methods.